1. Field of the Invention
The present invention relates to an alternating current (AC) light-emitting diode (LED) driving circuit and more particularly to a method and a device for dynamically controlling heat dissipation of an AC LED driving circuit.
2. Description of the Related Art
With reference to FIG. 8, an AC LED driving circuit has a full-bridge rectifier 50, an LED unit 51, a voltage-controlled transistor 52, a current detection unit 53 and a steady current control unit 54. The full-bridge rectifier 50 is connected to an AC power source. The AC power is rectified to a half-wave DC power and then outputted to the LED unit 51. As the voltage-controlled transistor 52 and the current detection unit 53 are connected in series to a power loop constituted by the half-wave DC power and the LED unit 51. Hence, the steady current control unit 54 can detect the magnitude of current flowing through the LED unit 51 through the current detection unit, further determine if the value of the current flowing through the LED unit 51 now is too large or too small relative to a reference current value, and adjust a bias voltage of the voltage-controlled transistor 51 to maintain the value of the current flowing through the LED unit 51 at a fixed level for the LED unit 51 to stably emit light.
As the foregoing AC LED driving circuit is a non-isolated driving circuit and has no capacitor or inductor therein, the AC LED driving circuit has an rather high overall power factor and conversion efficiency being effective in saving power. However, to keep a stable current flowing through the LED unit 51, the single-chip voltage-controlled transistor 52 used in the AC LED driving circuit to control electronic components of the LED unit 51 fails to be normally operated for the sake of being easily overheated when the LED unit with high wattage is applied.